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class="link-text" data-v-2cfe069a>01.基础入门</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/articles/rust/02.%E5%9F%BA%E7%A1%80%E8%AF%AD%E6%B3%95.html" style="padding-left:0px;" data-v-2cfe069a data-v-3c355974><!--[--><span class="link-text" data-v-2cfe069a>02.基础语法</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/articles/rust/03.%E6%8C%87%E9%92%88%E4%B8%8E%E5%86%85%E5%AD%98%E5%88%86%E9%85%8D.html" style="padding-left:0px;" data-v-2cfe069a data-v-3c355974><!--[--><span class="link-text" data-v-2cfe069a>03.指针与内存分配</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/articles/rust/04.%E7%A8%8B%E5%BA%8F%E7%BB%93%E6%9E%84%E5%92%8C%E5%BC%82%E5%B8%B8%E5%A4%84%E7%90%86.html" style="padding-left:0px;" data-v-2cfe069a data-v-3c355974><!--[--><span class="link-text" data-v-2cfe069a>04.程序结构和异常处理</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link active" 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server</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/articles/rustweb/02.Actix.html" style="padding-left:0px;" data-v-2cfe069a data-v-3c355974><!--[--><span class="link-text" data-v-2cfe069a>02.Actix</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/articles/rustweb/03.%E8%BF%9E%E6%8E%A5%E6%95%B0%E6%8D%AE%E5%BA%93.html" style="padding-left:0px;" data-v-2cfe069a data-v-3c355974><!--[--><span class="link-text" data-v-2cfe069a>03.连接数据库</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/articles/rustweb/04.%E9%94%99%E8%AF%AF%E5%A4%84%E7%90%86.html" style="padding-left:0px;" data-v-2cfe069a data-v-3c355974><!--[--><span class="link-text" data-v-2cfe069a>04.错误处理</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/articles/rustweb/05.%E5%AE%8C%E6%95%B4%E9%A1%B9%E7%9B%AE%E9%87%8D%E6%9E%84.html" style="padding-left:0px;" data-v-2cfe069a data-v-3c355974><!--[--><span class="link-text" data-v-2cfe069a>05.完整项目重构</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/articles/rustweb/06.%E6%9C%8D%E5%8A%A1%E5%99%A8%E7%AB%AFweb%E5%BA%94%E7%94%A8.html" style="padding-left:0px;" data-v-2cfe069a data-v-3c355974><!--[--><span class="link-text" data-v-2cfe069a>06.服务器端web应用</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/articles/rustweb/07.WebAssembly.html" style="padding-left:0px;" data-v-2cfe069a data-v-3c355974><!--[--><span class="link-text" data-v-2cfe069a>07.WebAssembly</span><!--]--><!----></a><!----><!--]--><!--[--><a class="VPLink link link" href="/articles/rustweb/08.%E5%8F%91%E5%B8%83.html" style="padding-left:0px;" data-v-2cfe069a data-v-3c355974><!--[--><span class="link-text" data-v-2cfe069a>08.发布</span><!--]--><!----></a><!----><!--]--><!--]--></div></section></div><!--]--></nav></aside><div class="VPContent has-sidebar" id="VPContent" data-v-c6a644e1 data-v-c95df128><div class="VPDoc has-sidebar has-aside" data-v-c95df128 data-v-37ebe389><div class="container" data-v-37ebe389><div class="aside" data-v-37ebe389><div class="aside-curtain" data-v-37ebe389></div><div class="aside-container" data-v-37ebe389><div class="aside-content" data-v-37ebe389><div class="VPDocAside" data-v-37ebe389 data-v-afc4c1a1><!--[--><!--]--><!--[--><!--]--><div class="VPDocAsideOutline" data-v-afc4c1a1 data-v-2865c0b0><div class="content" data-v-2865c0b0><div class="outline-marker" data-v-2865c0b0></div><div class="outline-title" data-v-2865c0b0>On this page</div><nav aria-labelledby="doc-outline-aria-label" data-v-2865c0b0><span class="visually-hidden" id="doc-outline-aria-label" data-v-2865c0b0> Table of Contents for current page </span><ul class="root" data-v-2865c0b0 data-v-1188541a><!--[--><!--]--></ul></nav></div></div><!--[--><!--]--><div class="spacer" data-v-afc4c1a1></div><!--[--><!--]--><!----><!--[--><!--]--><!--[--><!--]--></div></div></div></div><div class="content" data-v-37ebe389><div class="content-container" data-v-37ebe389><!--[--><!--]--><main class="main" data-v-37ebe389><div style="position:relative;" class="vp-doc _articles_rust_05_%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84%E4%B8%8E%E6%B3%9B%E5%9E%8B" data-v-37ebe389><div><h1 id="rust入门（五）：数据结构与泛型" tabindex="-1">Rust入门（五）：数据结构与泛型 <a class="header-anchor" href="#rust入门（五）：数据结构与泛型" aria-hidden="true">#</a></h1><p>rust提供了多种数据结构来帮助存储数据，他们都是可变长度的集合</p><h2 id="vector" tabindex="-1">Vector <a class="header-anchor" href="#vector" aria-hidden="true">#</a></h2><p>vector 允许我们以可变长度存储一系列相同的值，类似于可变长度的数组，它在创建时需要指定存储的数据的类型，或者指定初始值使得编译器能够分析出其中存储的类型</p><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#676E95;">//新建一个空的</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> v</span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">Vec</span><span style="color:#89DDFF;">&lt;</span><span style="color:#FFCB6B;">i32</span><span style="color:#89DDFF;">&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">Vec</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">new</span><span style="color:#89DDFF;">();</span></span>
<span class="line"><span style="color:#676E95;">//设置初始值</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> v </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">vec!</span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">];</span></span>
<span class="line"></span></code></pre></div><p>你可以将 vector 申明为可变的，这样就可以使用push方法可以向其中新增元素</p><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">mut</span><span style="color:#A6ACCD;"> v </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">Vec</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">new</span><span style="color:#89DDFF;">();</span></span>
<span class="line"><span style="color:#A6ACCD;">v</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">push</span><span style="color:#89DDFF;">(</span><span style="color:#F78C6C;">5</span><span style="color:#89DDFF;">);</span></span>
<span class="line"></span></code></pre></div><p>以下是一些其他api的使用方式</p><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#A6ACCD;">vec</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">is_empty</span><span style="color:#89DDFF;">()</span><span style="color:#676E95;">  //判空，返回bool值</span></span>
<span class="line"><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">].</span><span style="color:#82AAFF;">repeat</span><span style="color:#89DDFF;">(</span><span style="color:#F78C6C;">5</span><span style="color:#89DDFF;">)</span><span style="color:#676E95;">   //[1,1,1,1,1],一个1重复5次的vector</span></span>
<span class="line"><span style="color:#A6ACCD;">v</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">len</span><span style="color:#89DDFF;">()</span><span style="color:#676E95;">         //长度</span></span>
<span class="line"><span style="color:#676E95;">//追加一组数据</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">mut</span><span style="color:#A6ACCD;"> vec5 </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">].</span><span style="color:#82AAFF;">repeat</span><span style="color:#89DDFF;">(</span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">);</span></span>
<span class="line"><span style="color:#A6ACCD;">vec</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">append</span><span style="color:#89DDFF;">(&amp;</span><span style="color:#C792EA;">mut</span><span style="color:#A6ACCD;"> vec5</span><span style="color:#89DDFF;">);</span></span>
<span class="line"><span style="color:#676E95;">//追加一组数据</span></span>
<span class="line"><span style="color:#A6ACCD;">vec</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">extend</span><span style="color:#89DDFF;">([</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">].</span><span style="color:#82AAFF;">iter</span><span style="color:#89DDFF;">().</span><span style="color:#82AAFF;">copied</span><span style="color:#89DDFF;">());</span></span>
<span class="line"><span style="color:#676E95;">//删除</span></span>
<span class="line"><span style="color:#A6ACCD;">vec</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">remove</span><span style="color:#89DDFF;">(</span><span style="color:#A6ACCD;">vec</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">len</span><span style="color:#89DDFF;">()</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">-</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">);</span></span>
<span class="line"><span style="color:#676E95;">//排序</span></span>
<span class="line"><span style="color:#A6ACCD;">vec</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">sort</span><span style="color:#89DDFF;">();</span></span>
<span class="line"><span style="color:#676E95;">//寻找是否存在某个数据，返回下标bool</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> ss </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> vec</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">contains</span><span style="color:#89DDFF;">(&amp;</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">);</span></span>
<span class="line"></span></code></pre></div><p>再获取一个 vector 中的元素时，可以使用下标访问它，但是对于 String 等非标量的数据结构，直接访问它会发生所有权转移的问题</p><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#676E95;">//这是可以的</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> v </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">vec!</span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">];</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> third </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> v</span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">];</span></span>
<span class="line"><span style="color:#676E95;">//这是报错的</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> v </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">vec!</span><span style="color:#89DDFF;">[</span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">from</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">a</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">),</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">from</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">a</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">),</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">from</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">a</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">)];</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> third </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> v</span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">];</span></span>
<span class="line"></span></code></pre></div><p>为了解决这个问题，我们通过会引用 vector 中的元素在，引用 vector 的元素时，可以选择使用 &amp;引用或者 get 的方式来引用它，区别是 &amp;引用 是返回 vector中某个元素的引用，如果这个元素不存在，会发生越界的错误；而 get 函数返回一个 Option 指针 ，如果你访问的元素不存在不会产生问题：</p><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> v </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">vec!</span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">];</span></span>
<span class="line"><span style="color:#676E95;">//引用</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> third</span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&amp;</span><span style="color:#FFCB6B;">i32</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&amp;</span><span style="color:#A6ACCD;">v</span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">];</span></span>
<span class="line"><span style="color:#676E95;">//get函数</span></span>
<span class="line"><span style="color:#89DDFF;">match</span><span style="color:#A6ACCD;"> v</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">get</span><span style="color:#89DDFF;">(</span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">)</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#676E95;">    	//这里的third是一个指针</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#FFCB6B;">Some</span><span style="color:#89DDFF;">(</span><span style="color:#A6ACCD;">third</span><span style="color:#89DDFF;">)</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">=&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">println!</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">The third element is </span><span style="color:#89DDFF;">{}&quot;</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> third</span><span style="color:#89DDFF;">),</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#FFCB6B;">None</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">=&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">println!</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">There is no third element.</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">),</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"></span></code></pre></div><p>但是如果我们获取了 vector 中一个数的引用，再去改变这个 vector 可能会引发问题，因为改变 vector 可能会引发内存的重新发配，而引用的地址的信息可能因此发生改变，从而产生异常。你可以通过之前处理String 相同的克隆一份数据的方式来获取数据：</p><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#676E95;">//这样是报错的</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> v </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">vec!</span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">3</span><span style="color:#89DDFF;">];</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> third</span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&amp;</span><span style="color:#FFCB6B;">i32</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&amp;</span><span style="color:#A6ACCD;">v</span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">];</span></span>
<span class="line"><span style="color:#A6ACCD;">v</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">push</span><span style="color:#89DDFF;">(</span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">);</span></span>
<span class="line"></span>
<span class="line"><span style="color:#676E95;">//clone一份数据</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">mut</span><span style="color:#A6ACCD;"> v </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">vec!</span><span style="color:#89DDFF;">[</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">a</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">to_string</span><span style="color:#89DDFF;">(),</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">a</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">to_string</span><span style="color:#89DDFF;">(),</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">a</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">to_string</span><span style="color:#89DDFF;">()];</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">mut</span><span style="color:#A6ACCD;"> first </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> v</span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">0</span><span style="color:#89DDFF;">].</span><span style="color:#82AAFF;">clone</span><span style="color:#89DDFF;">();</span></span>
<span class="line"><span style="color:#A6ACCD;">v</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">push</span><span style="color:#89DDFF;">(</span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">from</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">aaa</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">));</span></span>
<span class="line"></span></code></pre></div><p>使用for循环可以遍历 vector 中的元素，因为是先引用再遍历，每一个 i 的返回值都是引用，如果数组可变，也可以返回可变的引用，通过 <code>*</code> 解引用的方式可以直接改变每一个引用指向的内容的数值，这个在后续会提到：</p><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> v </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">vec!</span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">100</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">32</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">57</span><span style="color:#89DDFF;">];</span></span>
<span class="line"><span style="color:#89DDFF;">for</span><span style="color:#A6ACCD;"> i </span><span style="color:#F78C6C;">in</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&amp;</span><span style="color:#A6ACCD;">v </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#82AAFF;">println!</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;{}&quot;</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> i</span><span style="color:#89DDFF;">);</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#676E95;">//可变数组的遍历</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">mut</span><span style="color:#A6ACCD;"> v </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">vec!</span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">100</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">32</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">57</span><span style="color:#89DDFF;">];</span></span>
<span class="line"><span style="color:#89DDFF;">for</span><span style="color:#A6ACCD;"> i </span><span style="color:#F78C6C;">in</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&amp;</span><span style="color:#C792EA;">mut</span><span style="color:#A6ACCD;"> v </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#89DDFF;">*</span><span style="color:#A6ACCD;">i </span><span style="color:#89DDFF;">+=</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">50</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"></span></code></pre></div><h2 id="string" tabindex="-1">String <a class="header-anchor" href="#string" aria-hidden="true">#</a></h2><p>在rust中有两种字符串：</p><ol><li><p>String就像是Vec一样是动态分配在堆heap上的字符串类型，它指向一串UTF8编码的字节序。使用一些 String 自带的api可以创建一个String。</p></li><li><p>&amp;str 是一个指向分配在某处的 String 的一个固定容量的视图，或者是一个使用 “ ” 定义的字符串字面量，不同的是前者指向String的内容，在堆上，后者指向静态内存，因为是引用，所以他没有字符串的所有权。</p></li><li><p>使用 to_string() 可以将str转换为 String</p></li><li><p>使用 [ a..b ] 可以将 String 转化成切片 ， 同时在 rust 中 &amp;String 可以直接转为 &amp;str 传入各个函数 api 中</p></li></ol><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#676E95;">//创建空字符串</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">mut</span><span style="color:#A6ACCD;"> s </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">new</span><span style="color:#89DDFF;">();</span></span>
<span class="line"><span style="color:#676E95;">//新建一个字符串</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> s </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">from</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">initial contents</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">);</span></span>
<span class="line"><span style="color:#676E95;">//创建一个字符串字面量 &amp;str</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> data </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">initial contents</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#676E95;">//转换成String</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> s </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> data</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">to_string</span><span style="color:#89DDFF;">();</span></span>
<span class="line"><span style="color:#676E95;">//转化为 &amp;str</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">str</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&amp;</span><span style="color:#A6ACCD;">s</span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">0</span><span style="color:#89DDFF;">..</span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">];</span></span>
<span class="line"><span style="color:#676E95;">//可以直接转化</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">str</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&amp;</span><span style="color:#A6ACCD;">s</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> e_0 </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">from</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">hello world</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">);</span><span style="color:#A6ACCD;"> </span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> e   </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> e_0</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">as_str</span><span style="color:#89DDFF;">();</span></span>
<span class="line"></span></code></pre></div><p>String 的大小可以增加，其内容也可以改变，可以通过 <code>push_str</code> 方法来字符串常量，从而使 <code>String</code> 变长，这个方法也可以使用 + 符号来实现，但是 + 符号的第二个参数需要是一个 &amp;str</p><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">mut</span><span style="color:#A6ACCD;"> s </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">from</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">foo</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">);</span></span>
<span class="line"><span style="color:#A6ACCD;">s</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">push_str</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">bar</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">);</span></span>
<span class="line"><span style="color:#676E95;">//上下的作用相同</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> s1 </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">from</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">foo</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">);</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> s2 </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">from</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">bar</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">);</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> s3 </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> s1 </span><span style="color:#89DDFF;">+</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&amp;</span><span style="color:#A6ACCD;">s2</span><span style="color:#89DDFF;">;</span><span style="color:#676E95;"> // 注意 s1 被移动了，不能继续使用</span></span>
<span class="line"></span></code></pre></div><p>使用 format! 可以快速拼接多个字符串</p><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> s1 </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">from</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">tic</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">);</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> s2 </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">from</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">tac</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">);</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> s3 </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">from</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">toe</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">);</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> s </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">format!</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;{}</span><span style="color:#C3E88D;">-</span><span style="color:#89DDFF;">{}</span><span style="color:#C3E88D;">-</span><span style="color:#89DDFF;">{}&quot;</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> s1</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> s2</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> s3</span><span style="color:#89DDFF;">);</span></span>
<span class="line"></span></code></pre></div><p>在rust中不能随意获取一个字符串中的一个字符串，因为 rust 使用 unicode 编码，所以有些语言一个字母不一定存一个字节，有时候是两个：</p><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> hello </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">from</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">Здравствуйте</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">);</span></span>
<span class="line"><span style="color:#A6ACCD;">hello</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">len</span><span style="color:#89DDFF;">();</span><span style="color:#676E95;"> // 24</span></span>
<span class="line"><span style="color:#676E95;">//因为第一个字母占两个字节，所以这类代码是不可以通过的</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> answer </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&amp;</span><span style="color:#A6ACCD;">hello</span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">0</span><span style="color:#89DDFF;">];</span></span>
<span class="line"><span style="color:#676E95;">//这样的代码是可以通过的，因为刚好截取了正确的字母</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> answer </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&amp;</span><span style="color:#A6ACCD;">hello</span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">0</span><span style="color:#89DDFF;">..</span><span style="color:#F78C6C;">2</span><span style="color:#89DDFF;">];</span></span>
<span class="line"><span style="color:#676E95;">//这样的代码是不可以通过的，因为刚好截取一个字母的一半</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> answer </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&amp;</span><span style="color:#A6ACCD;">hello</span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">0</span><span style="color:#89DDFF;">..</span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">];</span></span>
<span class="line"></span></code></pre></div><p>对于字符串可以使用不同的方式进行遍历，可以按照一个一个 unicode 字节或者一个一个字符进行遍历</p><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#89DDFF;">for</span><span style="color:#A6ACCD;"> c </span><span style="color:#F78C6C;">in</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">नमस्ते</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">chars</span><span style="color:#89DDFF;">()</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#82AAFF;">println!</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;{}&quot;</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> c</span><span style="color:#89DDFF;">);</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#676E95;">//按照字符遍历न , म ....</span></span>
<span class="line"><span style="color:#89DDFF;">for</span><span style="color:#A6ACCD;"> b </span><span style="color:#F78C6C;">in</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">नमस्ते</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">bytes</span><span style="color:#89DDFF;">()</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#82AAFF;">println!</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;{}&quot;</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> b</span><span style="color:#89DDFF;">);</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#676E95;">//按字节遍历 224 ,164.....</span></span>
<span class="line"></span></code></pre></div><h2 id="hashmap" tabindex="-1">HashMap <a class="header-anchor" href="#hashmap" aria-hidden="true">#</a></h2><p><code>HashMap&lt;K, V&gt;</code> 类型储存了一个键类型 <code>K</code> 对应一个值类型 <code>V</code> 的映射，其中的每个元素都按照 k，v 对的形式存储，根据唯一的 k可以找对应的 v ，可以使用 <code>new</code> 创建一个空的 <code>HashMap</code>，并使用 <code>insert</code> 增加元素，在第一次新增元素之后，编译器就会将 HashMap 的类型固定，不能再插入其他类型的键值对</p><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#F78C6C;">use</span><span style="color:#FFCB6B;"> std</span><span style="color:#89DDFF;">::</span><span style="color:#FFCB6B;">collections</span><span style="color:#89DDFF;">::</span><span style="color:#FFCB6B;">HashMap</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">mut</span><span style="color:#A6ACCD;"> a </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">HashMap</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">new</span><span style="color:#89DDFF;">();</span></span>
<span class="line"><span style="color:#A6ACCD;">a</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">insert</span><span style="color:#89DDFF;">(</span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">from</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">1</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">),</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">10</span><span style="color:#89DDFF;">);</span></span>
<span class="line"></span></code></pre></div><p>另一个构建哈希 map 的方法是在一个元组的 vector 上使用迭代器（iterator）和 <code>collect</code> 方法，其中每个元组包含一个键值对，这将在后续介绍。</p><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> t </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">vec!</span><span style="color:#89DDFF;">[</span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">from</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">a</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">),</span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">from</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">b</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">)];</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> i </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">vec!</span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">10</span><span style="color:#89DDFF;">,</span><span style="color:#F78C6C;">20</span><span style="color:#89DDFF;">];</span></span>
<span class="line"><span style="color:#676E95;">//必须有HashMap&lt;_,_&gt; ,collect可以返回多种数据结构</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> hash </span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">HashMap</span><span style="color:#89DDFF;">&lt;</span><span style="color:#A6ACCD;">_</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;">_</span><span style="color:#89DDFF;">&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> t</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">iter</span><span style="color:#89DDFF;">().</span><span style="color:#82AAFF;">zip</span><span style="color:#89DDFF;">(</span><span style="color:#A6ACCD;">i</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">iter</span><span style="color:#89DDFF;">()).</span><span style="color:#82AAFF;">collect</span><span style="color:#89DDFF;">();</span></span>
<span class="line"></span></code></pre></div><p>如果 insert 一个已经存在的 key 那么会直接更新它，所以可以使用 entry ( ) 和 or_insert( ) 函数进行检查 ， 这样的组合只有再某个key值不存在的时候才会插入，存在则不会改变值，同时它可以返回指定 key 的 val ，它是一个引用，如果想要改变它的值需要解引用</p><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> val </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">entry</span><span style="color:#89DDFF;">(</span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">from</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">1</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">)).</span><span style="color:#82AAFF;">or_insert</span><span style="color:#89DDFF;">(</span><span style="color:#F78C6C;">50</span><span style="color:#89DDFF;">);</span></span>
<span class="line"><span style="color:#89DDFF;">*</span><span style="color:#A6ACCD;">val </span><span style="color:#89DDFF;">+=</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">1</span><span style="color:#89DDFF;">;</span></span>
<span class="line"></span></code></pre></div><p>可以通过 <code>get</code> 方法并提供对应的键来从哈希 map 中获取值，返回 <code>Option&lt;V&gt;</code></p><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> t </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">String</span><span style="color:#89DDFF;">::</span><span style="color:#82AAFF;">from</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;</span><span style="color:#C3E88D;">1</span><span style="color:#89DDFF;">&quot;</span><span style="color:#89DDFF;">);</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> ta </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> a</span><span style="color:#89DDFF;">.</span><span style="color:#82AAFF;">get</span><span style="color:#89DDFF;">(&amp;</span><span style="color:#A6ACCD;">t</span><span style="color:#89DDFF;">);</span></span>
<span class="line"></span></code></pre></div><p>可以使用与 vector 类似的方式来遍历哈希 map 中的每一个键值对</p><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#89DDFF;">for</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">(</span><span style="color:#A6ACCD;">key</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> value</span><span style="color:#89DDFF;">)</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">in</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&amp;</span><span style="color:#A6ACCD;">a </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#82AAFF;">println!</span><span style="color:#89DDFF;">(</span><span style="color:#89DDFF;">&quot;{}</span><span style="color:#C3E88D;">: </span><span style="color:#89DDFF;">{}&quot;</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> key</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> value</span><span style="color:#89DDFF;">);</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"></span></code></pre></div><h2 id="泛型" tabindex="-1">泛型 <a class="header-anchor" href="#泛型" aria-hidden="true">#</a></h2><p>我们可以使用泛型为像函数签名或结构体这样的项创建定义，可以把它理解成是一个占位符，直到我们需要具体定义使用某个结构时，将具体的数据类型填充进去，所有使用泛型占位的地方都将成为该类型。使用泛型可以编写不重复的代码，而 Rust 将会为每一个实例编译其特定类型的代码。这意味着在使用泛型时没有运行时开销；当代码运行，它的执行效率就跟好像手写每个具体定义的重复代码一样。这个单态化过程正是 Rust 泛型在运行时极其高效的原因。</p><p>如以下的例子，T是那个泛型即占位符，传入一个 i32 的数组之后，T就改写为了 i32</p><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#676E95;">//泛型定义</span></span>
<span class="line"><span style="color:#F78C6C;">fn</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">largest</span><span style="color:#89DDFF;">&lt;</span><span style="color:#FFCB6B;">T</span><span style="color:#89DDFF;">&gt;(</span><span style="color:#A6ACCD;">list</span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&amp;[</span><span style="color:#FFCB6B;">T</span><span style="color:#89DDFF;">])</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">-&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">T</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> </span><span style="color:#C792EA;">mut</span><span style="color:#A6ACCD;"> largest </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> list</span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">0</span><span style="color:#89DDFF;">];</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#89DDFF;">for</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">&amp;</span><span style="color:#A6ACCD;">item </span><span style="color:#F78C6C;">in</span><span style="color:#A6ACCD;"> list </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#89DDFF;">if</span><span style="color:#A6ACCD;"> item </span><span style="color:#89DDFF;">&gt;</span><span style="color:#A6ACCD;"> largest </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;">            largest </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> item</span><span style="color:#89DDFF;">;</span></span>
<span class="line"><span style="color:#A6ACCD;">        </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#A6ACCD;">    largest</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> number_list </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">vec!</span><span style="color:#89DDFF;">[</span><span style="color:#F78C6C;">34</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">50</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">25</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">100</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#F78C6C;">65</span><span style="color:#89DDFF;">];</span></span>
<span class="line"><span style="color:#676E95;">//传入一个数字</span></span>
<span class="line"><span style="color:#C792EA;">let</span><span style="color:#A6ACCD;"> result </span><span style="color:#89DDFF;">=</span><span style="color:#A6ACCD;"> </span><span style="color:#82AAFF;">largest</span><span style="color:#89DDFF;">(&amp;</span><span style="color:#A6ACCD;">number_list</span><span style="color:#89DDFF;">);</span></span>
<span class="line"></span></code></pre></div><p>但是如果将数组变成字符串，则会产生报错，因为不能适用于 <code>T</code> 的所有可能的类型。因为在函数体需要比较 <code>T</code> 类型的值，不过它只能用于我们知道如何排序的类型。</p><p>在一个定义中，可以包含多个泛型，仅需要一一对应即可，在结构体、函数、枚举中都可以使用泛型</p><div class="language-rust"><button class="copy"></button><span class="lang">rust</span><pre><code><span class="line"><span style="color:#676E95;">//单个泛型</span></span>
<span class="line"><span style="color:#C792EA;">struct</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">Point</span><span style="color:#89DDFF;">&lt;</span><span style="color:#FFCB6B;">T</span><span style="color:#89DDFF;">&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;">    x</span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">T</span><span style="color:#89DDFF;">,</span></span>
<span class="line"><span style="color:#A6ACCD;">    y</span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">T</span><span style="color:#89DDFF;">,</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#676E95;">//多个泛型</span></span>
<span class="line"><span style="color:#C792EA;">struct</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">Point</span><span style="color:#89DDFF;">&lt;</span><span style="color:#FFCB6B;">T</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">U</span><span style="color:#89DDFF;">&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;">    x</span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">T</span><span style="color:#89DDFF;">,</span></span>
<span class="line"><span style="color:#A6ACCD;">    y</span><span style="color:#89DDFF;">:</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">U</span><span style="color:#89DDFF;">,</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"><span style="color:#676E95;">//枚举泛型</span></span>
<span class="line"><span style="color:#C792EA;">enum</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">Result</span><span style="color:#89DDFF;">&lt;</span><span style="color:#FFCB6B;">T</span><span style="color:#89DDFF;">,</span><span style="color:#A6ACCD;"> </span><span style="color:#FFCB6B;">E</span><span style="color:#89DDFF;">&gt;</span><span style="color:#A6ACCD;"> </span><span style="color:#89DDFF;">{</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#FFCB6B;">Ok</span><span style="color:#89DDFF;">(</span><span style="color:#FFCB6B;">T</span><span style="color:#89DDFF;">),</span></span>
<span class="line"><span style="color:#A6ACCD;">    </span><span style="color:#FFCB6B;">Err</span><span style="color:#89DDFF;">(</span><span style="color:#FFCB6B;">E</span><span style="color:#89DDFF;">),</span></span>
<span class="line"><span style="color:#89DDFF;">}</span></span>
<span class="line"></span></code></pre></div></div></div></main><!--[--><!--]--><footer class="VPDocFooter" data-v-37ebe389 data-v-a54a85bd><!----><div class="prev-next" data-v-a54a85bd><div class="pager" data-v-a54a85bd><a class="pager-link prev" href="/articles/rust/04.%E7%A8%8B%E5%BA%8F%E7%BB%93%E6%9E%84%E5%92%8C%E5%BC%82%E5%B8%B8%E5%A4%84%E7%90%86.html" data-v-a54a85bd><span class="desc" data-v-a54a85bd>Previous page</span><span class="title" data-v-a54a85bd>04.程序结构和异常处理</span></a></div><div class="has-prev pager" data-v-a54a85bd><a class="pager-link next" href="/articles/rust/06.trait%E4%B8%8E%E7%94%9F%E5%91%BD%E5%91%A8%E6%9C%9F.html" data-v-a54a85bd><span class="desc" data-v-a54a85bd>Next page</span><span class="title" data-v-a54a85bd>06.trait与生命周期</span></a></div></div></footer><!--[--><!--]--></div></div></div></div></div><!----><!--[--><!--]--></div></div>
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